1. Field of the Invention
This invention relates to additives for sodium bromide compositions and particularly, to additive mixtures which eliminate floc formation in sodium bromide brines and insure that solid sodium bromide flows freely.
2. Description of the Prior Art
Aqueous solutions of alkali and alkaline earth metal and zinc halides, and mixtures thereof, are commonly used as drilling, completion, packer and perforating media in oil and gas wells. Depending on the formation pressures encountered in the well, fluids with densities between 8.5 and 21.0 lb/gal are designed to provide a hydrostatic head to balance formation pressures. The advent of the so-called solids-free brines in recent years has greatly improved the completion and workover activities by eliminating formation plugging and solids settling problems previously encountered when water-based and oil-based drilling fluids were used.
Although the introduction of these various new completion fluids has helped resolve many of the difficulties encountered in completion and workover operations, problems still remain. For example, use of completion fluids contaminated with alkaline earth and transition metal ions in subterranean wells containing carbonates and sulfates results in precipitation of metal carbonates and sulfates. Further, it has been reported by Shaughnessy, et al, in "Workover Fluids for Prudhoe Bay", Exxon Report No. 3187, February-July 1977, that the mixing of calcium chloride workover fluids with formation brines under certain conditions (i.e., at a pressure of 5000 psi and a temperature of 220.degree. F.) can lead to the precipitation of calcium carbonate within reservoir rock resulting in formation damage. These problems have heretofore been resolved, at least for shallow wells, by utilizing sodium bromide completion and workover fluids in place of calcium ion containing solutions.
Sodium bromide solutions used as completion and workover fluids, have a pH range between 6.5 and 7.5. At these pH values, small concentrations of alkaline earth and transition metal ions in sodium bromide stay in solution and may go unnoticed at the time sodium bromide fluids are utilized. However, when such sodium bromide fluids are used in wells with formation brines at high pH and high carbon dioxide content, precipitation of metal carbonates and hydroxides can lead to formation damage.
Moreover, sodium bromide fluids prepared from "by-product" or "recycle" brines usually contain small concentrations of organic and inorganic materials. The organic materials, such as phenols and substituted phenols, are removed by passing the fluid through an activated carbon bed. However, it is also desirable to remove or solubilize low concentration inorganic contaminants (e.g. Ca.sup.2+, Mg.sup.2+, Al.sup.3+, Fe.sup.2+, Zn.sup.2+, Ni.sup.2+) which are also present in such recycle brines.
Sodium bromide solutions used as completion and workover fluids may be formulated in the field from solid sodium bromide. In addition, solid sodium bromide is also used as a weighting additive for brines. In order to be successfully used, such sodium bromide should be free flowing.
Amides of nitrilotriacetic acid have been used as anti-caking additives for sodium chloride produced by crystallization processes. It is believed that these amides significantly modify the crystal habits of sodium chloride and therefore act as crystal growth inhibitors or anti-caking agents. British Patent Specification No. 1,003,216 teaches that sodium chloride crystals obtained by crystallizing sodium chloride from a brine in the presence of nitrilotriacetamide, N=(CH.sub.2 CONH.sub.2).sub.3, are three dimensional dendrites having a low caking tendency. Methods for inhibiting the caking of inorganic salts are also taught by L. Phoenix, British Chemical Engineering, Vol.II, No. 1 Jan. 1966), pp.34-38. In addition, U.S. Pat. Nos. 2,990,246. Scott et al; 3,856,922, Bragdon; 3,987,077, Bragdon et al, teach the use of different amides of nitrilotriacetic acid for modifying the appearance or the crystal habits of sodium chloride leading t its reduced caking tendency.
A mixture of mono- di- and triamides of nitrilotriacetic acid has been used to reduce the caking tendency of sodium bromide produced by a spray drying process. However, because sodium bromide is not produced by crystallization, it is unlikely that these amides act as crystal habit modifiers for NaBr. It is believed that the amides of nitrilotriacetic acid act as a surface binder for NaBr and therefore prevent it from caking.
None of the prior art for sodium chloride mentioned above teaches the use of amides of NTA in combination with sodium tartrate as antifloc and anticaking additives for sodium bromide solution and spray dried sodium bromide produced from the solution.
Accordingly, a primary object of the present invention is to provide an additive mixture for sodium bromide fluids capable of solublizing metal carbonate and metal hydroxide precipitates.
A further objective of the present invention is to find a suitable solubilizing additive which can effectively form soluble compounds with alkaline earth, transition, and aluminum metal ions in the pH range of 6-12.
A related object is to provide a combination of additives of the character described which insures that sodium bromide solids flow freely.